1. are using a calibrated system and
2. meter on a subject
3. expose at the suggested meter reading
4. develop the film 'normally'
5. and print according to a calibrated, standard method

In Zone System parlance, to meter on a subject area and to expose using
the recommended meter reading is to place the subject area
on Zone V -- in the middle of the grayscale.

What happens
if you meter on a subject and modify the meter's recommendation
by overexposing 1 f-stop? Or underexposing 1 f-stop? Or over
or underexposing by more than 1 f-stop?

We will attempt to answer the question above by appealing to something that could be called photographer's common sense. It is a straightforward reasoning of the situation using unsophisticated logic and our existing knowledge of photography. (Developing this common sense can take a long time. In fact, very often photographers have developed bad thinking habits and inaccurate paradigms of how photographic concepts inter-relate. In those instances, good accurate common sense takes longer to cultivate)

drum roll please:  Here Goes.

Under conditions of

Normal Development and Printing

If we expose a subject area giving as exactly as much light to that subject area as the meter recommends, the subject will reproduce as middle gray.

If we expose a subject area giving more light to that subject than the meter recommends, the subject area will reproduce lighter than middle gray.

If we expose a subject area giving less light to that subject than the meter recommends, the subject area will reproduce darker than middle gray.

The insight above is most of what is needed to answer the question posed earlier. If, under conditions of a calibrated system, using Normal filmspeed, development and printing, we over-expose a subject area by one stop, the subject area will be reproduced lighter on the print. In Zone System parlance, to meter on a subject area,and over-expose by one F-stop is said to place the subject area on Zone VI. The placement is said to be Zone VI because it differs from a Zone V placement by one F-stop of exposure in the direction of white along the gray scale.

If, under conditions of a calibrated system, using Normal filmspeed, development and printing, we under-expose a subject area by one stop, the subject area will be reproduced darker on the print. In Zone System parlance, to meter on a subject area,and under-expose by one F-stop is said to place the subject area on Zone IV. The placement is said to be Zone IV because it differs from a Zone V placement by one F-stop of exposure in the direction of black along the gray scale.

Overexposing or underexposing by more than one F-stop moves a subject further from middle gray toward one end of the gray scale.

If over-exposing, the subject is placed somewhere between middle gray and white. 1,2,3,4 and 5 F-stops of overexposure place a subject on Zone VI, Zone VII, Zone VIII, Zone IX and Zone X respectively.

If under-exposing, the subject is placed somewhere between middle gray and black. 1,2,3,4 and 5 F-stops of underexposure place a subject on Zone IV, Zone III, Zone II, Zone I and Zone 0 respectively.